Idling speed control for stirling cycle engine

ABSTRACT

An idling speed control is provided for a Stirling cycle engine wherein a variable volume working space is provided by a selectively controlled series of dead volume chambers. The idling speed control comprises a dual action system loading the engine in response to (1) a governor speed setting by coupling an electrical generator loaded by a heater resistor in the air flow path to the burner to increase shaft load and (2) a temperature responsive feedback system to decrease the supply of fuel and air to the burner when said heater raises the temperature.

United States Patent [191 Hakansson IDLING SPEED CONTROL FOR STIRLING CYCLE ENGINE [75] Inventor: Sven Anders Samuel Hakansson,

Malmo, Sweden [73] Assignee: Kommanditbolaget United Stirling (Sweden) AB & Co., Malmo, Sweden [22] Filed: June 23, 1972 [21] Appl. No.: 265,626

[30] Foreign Application Priority Data July 7, 1971 Great Britain 31,822/71 [52] US. Cl. 60/24, 290/40 A [51] Int. Cl. F03g 7/06 [58] Field of Search 60/24; 290/40 A;

[56] References Cited UNITED STATES PATENTS 2,011,859 8/1935 Kalin 290/40 A 1 Jan. 1,1974

2,076,588 4/1937 Pearson 290/40 A 2,273,407 2/1942 Lilja 2,799,783 7/1957 McFarland 290/40 F FOREIGN PATENTS OR APPLICATIONS 173,767 1/1953 Austria 322/29 Primary Examiner-Martin P. Schwadron Assistant Examiner-H. Burks, Sr. Attorney-Laurence R. Brown [57] ABSTRACT An idling speed control is provided for a Stirling cycle engine wherein a variable volume working space is provided by a selectively controlled series of dead volume chambers. The idling speed control comprises a dual action system loading the engine in response to (1) a governor speed setting by coupling an electrical generator loaded by a heater resistor in the air flow path to the burner to increase shaft load and (2) a temperature responsive feedback system to decrease the supply of fuel and air to the burner when said heater raises the temperature.

5 Claims, 1 Drawing Figure IDLING SPEED CONTROL FOR STIRLING CYCLE ENGINE This invention relates to a Stirling cycle hot gas engine power-control system of the kind (herein called the kind defined) in which one or more dead volume chambers of different sizes may be connected to a working space in the engine, the fuel supply to a burner heating the engine working gas being governed by a temperature-responsive device to maintain a substantially constant temperature in the high temperature part of the engine.

Power-control systems of the kind defined have several advantages regarding quick response to changes in load and reliability in operating, but they have the drawback that a decrease in engine power output down to idling or zero output is not possible with dead volume chambers of moderate sizes.

The present invention is intended to provide a powercontrol system of the kind defined which makes it readily possible to obtain a constant low engine speed during idling.

According to the invention a power-control system of the kind defined is characterized in that coupled to a shaft driven by the engine is an electric generator connected in a circuit including a resistor mounted in an air delivery duct loading combustion air to the burner, a speed-responsive device being provided for completing the said circuit only if the engine speed exceeds a predetermined speed during idling of the engine.

The scope of the monopoly sought is defined in the Claims hereinafter, and how the invention may be put into practice is described in more detail with reference to the accompanying drawing showing by way of example a diagram of a power-control system according to the invention.

in the diagram a cylinder 1 of a Stirling cycle engine accommodates a displacer piston 2 rigidly connected to a piston rod 3 and a working piston 4 rigidly connected to a piston rod 5. Below the piston 2 a low temperature working chamber 6 is formed in the engine. This low temperature working chamber 6 is in communication with a high temperature working chamber 7 above the displacer piston 2 through a cooler 8 and a heat regenerator 9.

The low temperature working chamber 6 also communicates with a dead volume chamber 10 through a non-return valve 11 which always allows flow of gas in the direction from the dead volume chamber 10 into the working chamber 6. However, the non-return valve 11 is actuated by a spring 12 in the direction towards a fully open position. A solenoid 13 when energized overcomes the force of said spring 12 and keeps the valve 11 in a position in which flow of gas into the dead volume chamber 10 is prevented.

Four chambers l4, l5, l6 and 17 communicate individually with the dead volume chamber 10 through four respective valves of the same type as the valve 11 described above. The solenoids of the four valves may be! energized according toa program which for illustration purposes is shown to be effected by means of a sliding contact member 18 engaging a commutator 19.

in the position of the contact member 18 shown in the diagram none of the solenoids of the valves to the chambers 10 and 14 17 is energized and thus all these valves are open. Thus the dead volume chambers communicating with the working chamber 6 have an effective combined volume of maximum size.

in the position shown of the contact member 18 the idling position the contact member 18 will give a signal to actuate a frequency-controlled speed governor GOV designed for connecting a generator G to a resistor R adapted to be cooled by a flow of combustion air delivered through an air delivery duct from a blower 20 to a burner 21. A temperature-responsive device 22 gives a signal which is amplified in an amplifier AMPL and governs the supply of fuel and air to the burner 21.

The illustrated power-control system will operate as follows:

Various engine power outputs may be obtained by moving the sliding contact member 18 along the commutator 19. An upwards movement wil cause increase in engine power output by energizing one or more of the solenoids and thus actuating corresponding nonreturn valves to remain closed. The effect of actuating a non-return valve will be that minimum gas pressure will prevail in the dead volume chamber appertaining to each such valve and thus this chamber is rendered ineffective as a dead volume chamber.

If, for example, the valve 11 is actuated to become a non-return valve all the chambers 10 and 14 17 will contain gas at a constant pressure corresponding to the minimum pressure which occurs during each Stirling cycle. All pressure variations during each Stirling cycle will take place only in the low temperature and the high temperature working chambers 6 and 7 respectively and in their directly connecting conduits including the cooler 8 and the regenerator 9.

During idling, corresponding to the illustrated position of the sliding contact member 18, the speed governor GOV will connect the generator G to the resistor R in case the engine speed exceeds a predetermined idling speed to which the governor GOV is set. This means that a load is instantly put on the engine shaft and thus the speed of the engine will decrease. As soon as the speed of the engine has decreased to a speed below that to which the governor GOV is set, the generator G and the resistor R are disconnected and the engine shaft is released from the load. However, due to the fact that the power generated by the generator G is converted into heat energy imported to the combustion air conveyed to the burner 21, the temperature in the hot parts of the engine will rise and this will be registered by the temperature-responsive device 22 which consequently will give a signal'causing a decrease in the rate of supply of fuel to the burner 21.

Thus a power-control system according to the invention will cause a rapid response to signals from the speed governor during idling and there will be little or no hunting or variation in the engine idling speed.

I claim:

1. A Stirling cycle hot gas engine power control system comprising in combination, a power shaft driven by said engine, an electric generator connected to said power shaft to load the engine, an air delivery duct to supply combustion air to said engine, a heater resistor located in said duct and coupled to said generator, and speed responsive switching means connecting said resistor to said generator when the engine speed exceeds a predetermined speed.

2. A system as defined in claim 1 wherein the engine is provided with a working space and a control system including a plurality of dead volume chambers, a valve tween said plurality of chambers and said working space, and means selectively operating the control valve of said further chambers.

5. A system as defined in claim 1 including temperature sensing means responsive to changes of air temperature in said duct, and control means reducing the flow of fuel to said engine when the air temperature is increased. 

1. A Stirling cycle hot gas engine power control system comprising in combination, a power shaft driven by said engine, an electric generator connected to said power shaft to load the engine, an air delivery duct to supply combustion air to said engine, a heater resistor located in said duct and coupled to said generator, and speed responsive switching means connecting said resistor to said generator when the engine speed exceeds a predetermined speed.
 2. A system as defined in claim 1 wherein the engine is provided with a working space and a control system including a plurality of dead volume chambers, a valve coupling each said chamber with said working space of said engine, and means selectively operating said valves to control the effective size of said working space.
 3. A system as defined in claim 2 wherein each valve is spring biased in an open position, and said means operating the valves close them to act as a non-return valve allowing flow of gas only in the direction out of the respective dead volume chambers.
 4. A system as defined in claim 2 including a further dead volume chamber and control valve coupled between said plurality of chambers and said working space, and means selectively operating the control valve of said further chambers.
 5. A system as defined in claim 1 including temperature sensing means responsive to changes of air temperature in said duct, and control means reducing the flow of fuel to said engine when the air temperature is increased. 